The present invention relates to a rotary cutting apparatus usable more particularly in printing and forming lines of cardboard collapsible boxes and self-adhesive labels.
These apparatus are generally based on the rolling principle on one another of two superimposed cylinders of parallel axes, of which one, namely the cutting cylinder as such, is engraved in relief, while the other one or "anvil" cylinder is smooth. However, in some processes, the two cylinders can present complementary engravings. The driving into rotation of the two cylinders, at the same peripheral speed but in reverse directions, is provided by connection gears of same working diameter chosen in such manner that there remains, between the two cutting cylinders, a small constant distance necessary for providing a good cut of the cardboard or paper sheet passing therebetween, without however a contact between the metallic parts ensuring the cut.
The interval separating the two cutting cylinders of parallel axes is provided by rollers or raceways which are secured at both ends of the two cutting cylinders while being perfectly concentric therewith. The diameter of each of these rollers is equal to the working diameter of the connection gear. Thus the cutting pressure can be applied without reservation on the two cylinders.
The diameter of the cutting cylinders, which depends on the cut-out format, has also to be determined, as a function of the paper width, in such manner that the deflections appearing during the cut, added to the manufacturing tolerances, are not superior to the theoretical distance separating the cutting parts. The deflections which appear during the cutting operation have two origins : the deflection as such of the cylinders under the effect of a load which is punctual or uniformly distributed due to the cutting effort, and the deflection caused by the flexing moments due to the effort exerted on the cylinder spindles.
Yet, it is necessary, mainly for certain works requiring a great precision and a cut which is clean and without dust, to maintain a deflection, that is a camber of the cutting cylinder which is as small as possible during the cutting operation as such. In order to reduce this camber or deflection of the cutting cylinder, it is of course possible to consider using a cutting cylinder of large diameter, but this entails a high cost for the tooling and reception structure.
As disclosed in French patent 2,645,790, it has also been provided to suppress the second deflection, that is the deflection caused by the flexing moments, by using a particular disposition of the hydraulic jacks.
In "IRON AND STELL ENGINEER", vol. 46, no. 12, December 1969, Pittsburgh US pages 69-87, M. D. Stone has disclosed a Backup Roll Bending for Crown and Gage Control using counter flexing means currently used in rolling mills, and utilizing counter pressure cylinders.
In the above device, the main force is applied on the bearing blocks and the counter-flexion is obtained by a spacing apart of the spindles.
The prior art has also shown U.S. Pat. No. 4,608,895 J. L. Bell et al. and U.S. Pat. No. 4,732,082 C. Ireton ; as well as German patent application published under No 1,243,000 F. L. Smithe Machine Company ; French patent application published under No 21578,193 J. Lacan ; and British patent specification No 398,169 A. Bingham et al.